CARBONYL IRON
TABLE β Common Iron Preparations
Percentage of
Compound elemental iron
Ferrous sulfate 20
Ferrous fumarate 33
Ferrous gluconate 12
Ferric pyrophosphate 30
Ferrocholinate 14
Ferroglycine sulfate 16
Ferrous sulfate, dried 33
Ferrous carbonate, anhydrous 38
Carbonyl iron 100
Marx: Rosen's Emergency Medicine: Concepts and Cnoical Praclice, 5th eu.,
Rakel: Conn's Current Therapy 2002,54th ed.,Pg:358
Carbonyl Iron
More recently, a new approach to iron repletion has become available with the
identification of carbonyl iron as an effective therapy for iron deficiency. This iron
preparation is a bioavailable form of elemental iron that has long been used for iron
fortification of foods. It has a considerable advantage over iron salts in terms of safety
because it is markedly less toxic and carries a much lower risk of poisoning in children.
For these reasons, carbonyl iron is our first choice for oral iron therapy. We recommend
the administration of 150 mg daily in three divided doses of 50 mg each. Carbonyl iron
has an efficacy similar to that of other oral iron preparations in correcting iron deficiency
and the same principles out lined earlier for evaluating the response to therapy with iron
salts are applicable to treatment with carbonyl iron. Some patients notice a metallic taste
during carbonyl iron therapy. Iron deficiency anemia can be treated effectively with
lower total daily doses of carbonyl iron (50 to 100 mg), but a longer duration of therapy
may be needed at these doses to achieve iron repletion.
ROLE OF CARBONYL IRON : the plethora of disadvantages of conventional iron formulations, made it essential to rethink drug delivery strategies and carbonyl iron was intro
duced. Elemental uncharged iron powder was used
early in this century for treatment of iron deficiency
anaemia and was nontoxic when compared to fer-
rous salts. However, this elemental iron prepara-
tion, which was produced by a hydrogen-reduction
process, had poor bioavailability when compared lo
ferrous salts, possibly due to the relatively large size
of the iron particles of about 50CII"and relatively
limited reactive surface area. "Since then the el-
emental iron preparation known as carbonyl iron
powder has been introduced.
BWAVAILABIUTY OF CARBONYL
"Carbonyl" does not refer to the composition of
the iron particles but rather lo the manufacturing
process in which the controlled heating of vapor-
ized iron pentacarbonyl leads to the deposition of
uncharged, elemental iron as submicroscopic crys-
tals that form microscopic spheres of less than
5mic mm in diameter. The preparation is more than
98% pure. As a food additive, carbonyl iron has
been shown to he well absorbed and utilized for
haemoglobin synthesis, both in experimental ani-
mals and in humans. In Sweden, where about
half of the fortification iron now used is carbonyl
iron. the high bioavailability of this form of iron
has been considered one factor contributing lo a
reduction in iron deficiency. Recent studies in
rats have clarified the mechanism of absorption of
the finely particulate carbonyl iron now available
(Huebers et el. unpublished observations). The
conversion of particulate carbonyl iron to soluble
ionized iron by stomach acid was prerequisite for
absorption and was limited by the rate of gastric
acid production. Subsequent uptake by the intesti-
nal mucosa and absorption were similar with equiva-
lent doses of ferrous iron. although absorption of
carbonyl iron occurred over a longer interval. In
these studies, the bioavailability of carbonyl iron
and ferrous iron was similar with doses of 0.2 to
80 mg Fe/kg body weight.
Drug interaction:
Compounds containing calcium and magnesium, in-
cluding antacids and mineral supplements, and bi-
carbonates, carbonates, oxalates or phosphates.
may also impair the absorption of iron by the forma-
tion of insoluble complexes. Similarly the absorp-
tion of both iron salts and tetracyclines is diminished
when they are taken concomitantly by mouth. If
treatment with both drugs is required, a time interval
of about 2 to 3 hours should be allowed between
them. A suitable interval is also advised if an iron
supplement is required in patients receiving trien-
tine. Zinc salts may decrease the absorption of iron.
Some agents, such as ascorbic acid and citric acid.
may actually increase the absorption of iron.
The response to iron may be delayed in patients re-
ceiving concomitant parenteral chloramphenicol
therapy.
Iron salts can also decrease the absorption of other
drugs and thus reduce their bioavailability and clin-
ical effect. Drugs so affected included bisphospho-
nates, fluoroquinolones, levodopa, methyldopa,
penicillamine and tetracycline. Iron salts may re-
duce the efficacy of thyroxine.
EFFICACY AMD SAFETY
While not previously used pharmacologically, sev-
eral studies' suggest that as a therapeutic agent,
carbonyl iron powder may effectively correct iron
deficiency anaemia yet be considerably less toxic
than iron salts. In rats with iron deficiency anaemia.
carbonyl iron has been used successfully to cor-
rect anaemia and replace iron stores. In hu-
mans, as in dogs, rabbits, and guinea pigs, the
estimated lethal dose of oral ferrous sulfate is
about 200 mg Fe/kg body weight.
CONCLUSION
Iron deficiency remains a major health risk World-
wide. Physicians involved in the primary care and
in the obstetric and gynecologic care of women of
all ages must be aware of the nature of the problem
and the correct approach to screening, diagnosis.
and treatment. The potential benefit lo newborns
and infants and to their mothers is substantial.
Carbonyl iron is a safe. effective, well-tolerated
and inexpensive therapy for iron deficiency
anaemia. Patients with mild anaemia may correct
anaemia and rebuild iron stores with even a short
course of carbonyl iron.
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